World Journal of Microbiology and Biotechnology, 8, 160-163
Seasonality and toxigenicity of Vibrio cholerae non-01 isolated from different components of pond ecosystems of Dhaka City, Bangladesh M.S. Islam,* M.J. Alam and P.K.B. Neogi Diarrhoea due to Vibrio cholerae non-01 is common in Bangladesh. Four hundred and eighty samples, including plants, water, phytoplankton and sediment, were collected from five ponds in Dhaka every 15 days for one year. V. cholerae non-01 was isolated from 181 (38%) of the samples. Two peaks were evident: one in April and the other in August/September. Forty-three (23%) of the 181 isolates were examined for toxigenicity and 19% were cytotoxic to Y1 adrenal cells. This study provides evidence of the likely infectious nature of some ponds and may have relevance to the epidemiology of diarrhoea caused by V. cholerae non-01 in Bangladesh. Key words: Diarrhoea, seasonality, toxigenicity, Vibrio.
Vibrio cholerae non-01 is a causative agent of moderate-tosevere, cholera-like diarrhoea in Bangladesh and other parts of the world (Mclntyre el al. 1965; Zafari el al. 1973; Hughes et al. 1978). Strains of V. cholerae non-01 are morphologically and biochemically similar to those of V. cholerae 01 but are distinguished by lack of agglutination with group 01 antiserum (ColweU et al. 1977). Food-borne and water-borne outbreaks due to V. cholerae non-01 have been reported from various countries, including Czechoslovakia, Sudan, Saudi Arabia and India (Aldova et al. 1968; Zafari et al. 1973). Epidemics due to V. cholerae non-01 have also been reported during cholera outbreaks (Mclntyre et al. I965; Dutt et al. 1971). These organisms have been isolated from septicaemic and meningoencephalitis patients (Prats el al. 1975). The enterotoxigenicity of V. cholerae non-01 demonstrated in the rabbit ileal loop (RIL) assay and by other methods indicates that these strains are potential pathogens (Zinnaka & Carpenter 1972). The enterotoxin produced by V. cholerae non-01 is closely related to cholera toxin produced by classical V. cholerae 01 (Kaper et al. 1979). The ecology of V. cholerae non-01 has been studied in
M. S. Islam and P. K. B. Neogi are with the international Center for Diarrboeal Diseases Research, Bangladesh, GPO Box 128, Dhaka 1000, Bangladesh. M. J. Alam is with the Department of Microbiology, University of Dhaka, Bangladesh. *Corresponding author.
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World ]ournaI of Microbiology and Biotechnology, Vol 8, 1992
the Chesapeake Bay and California coastal waters (Colwell el al. 1977; Kenyon el al. 1984). These studies demonstrated a link between the number of organisms and water temperature. In Bangladesh, Khan et a]. (1984), in investigating the role of surface water as a possible reservoir of V. cholerae non-01 in the environment, found the bacteria in approximately 30% of samples tested. However, other components such as plants, plankton and sediment were not evaluated as possible reservoirs nor was the seasonality of the organisms documented. Moreover the organisms recovered were not examined for virulence factors. Therefore, in the present study we examined the seasonality of V. cholerae non-01 in the various components of the aquatic environment in addition to surface water and evaluated the toxigenicity of the isolated strains.
Materials and Methods Description of Ponds The surface area and depth of all ponds ranged from 1900 to 6000 m2 and 1.5 to 5.2 m, respectively. The water temperatures varied from 18 to 34~ and the salinities from O to 0.18~oo. In all except pond No. 1, the waters were alkaline and used by large numbers of people every day for bathing and washing. All ponds were over-flooded during the 1988 flood.
M.S. Islam, M.]. Alam and P.K.B. Neogi inoculation, animals were sacrificed and the results were expressed as the accumulated fluid volume in ml per cm of loop.
Collection of Samples Samples of water, plants, phytoplankton and sediments from five ponds in and around Dhaka city, Bangladesh, were collected every 15 days, between May 1988 and April 1989. Plants (Eichhornia crassipes, Nympkoides sp. and Telanthera philoxeroides) were collected and kept in polyethylene bags. Samples of water, each of 500 ml, were collected in pre-sterilized 500 ml narrow-mouth, plastic bottles. Phytoplankton was collected using plankton nets and kept in 120 rnl glass bottles. All field samples were transported to the laboratory inside an insulated ice-box with cool packs and processed within 6 h of collection. Sediment was collected with a core sampler and kept in 120 ml glass bottles.
GM1 ELISA. The presence of cholera toxin was assayed using the
GMIganglioside ELISAaccording to the method described by Sack et al. (1980). YI Adrenal Cell Assay. The filtrates were added to Y1 adrenal cells plated in 96-well plates 24 h previously and incubated at 37~ in 7% CO 2, as described by Sack & Sack (1975). After 24 h, cells were examined for cytotoxic and cytotonic effects.
Processing of Samples Plant material (10 g) was homogenized in 100 ml of sterile 0.9% saline in a Waring blender. Phytoplankton samples (I0 ml) were homogenized in a Teflon-tipped tissue grinder (Wheaton Scientific, Millville, NJ) using a Sted Fast stirrer (Model 300, Fisher Scientific, USA). One ml of the plant homogenate, 10 ml of phytoplankton homogenate, 50 ml of each water sample and 1.0 g of sediment were enriched separately in bile salts peptone broth and incubated overnight at 37~ All samples were then plated onto thiosulphate citrate bile salts sucrose (TCBS) agar and taurocholate tellurite gelatin agar and incubated at 37~ for 18 to 24 h (Monsur 1961). Suspected vibrio colonies were further characterized using standard procedures (West & Colwell 1984; Lee 1985). Enterotoxin Assays Bacterial Isolates. Forty-three isolates of 17. cholerae non-01 were selected randomly and tested for toxigenicity using three assays. The strains were isolated from plants, water, phytoplankton and sediment samples. Preparation of Culture Filtrates. The test strains were each grown in 10 ml of Richardson's medium in 50 ml conical flasks (Richardson 1969). The flasks were incubated in a shaking water bath with 100 rev/min for 16 h at 37~ The cultures were centrifuged at 10,000 x g for 30 min. The supematants were filtered through 0.22 pm pore membrane filters and stored at -20~ for use in the following assays. Rabbit ileal Loop (RIL) Assay. One ml of culture filtrate from each of the test strains was inoculated into a 4 to 6 cm length of ileal loop from 1.5 to 2.0kg New Zealand white rabbits (De & Chatterjee 1953). Each strain was tested in duplicate. Vibrio cholerae 01 strain 569B was used as a positive control. Eighteen hours after
Results Vibrio choIerae non-01 was isolated from 18I (38%) of the 480 environmental samples collected (Table I), of which pond No. 5 had the highest isolation rate of 62 from 96 samples collected (65%). In contrast, no organisms were recovered from any of the 96 samples collected from pond No. i. Pond No. 5 also yielded most organisms in each of the four sample types: 87% of water samples, 80% of phytoplankton, 67% of the plants and 25% of the soil sediment samples were positive (Table 1). The toxigenicities of 43 strains randomly selected for testing are shown in Table 2. Twelve strains isolated from plants, 12 from water, 11 from phytoplankton and eight from soil were tested. Overall, eight strains (19%) were cytotoxic for Y1 adrenal cells. No cytotonic activity was detected in the Y1 adrenal cell assay. All strains were also negative in the GM~ ELISA and RIL assays. Distinct seasonal patterns of isolation of V. cholerae non-01 in the four components of the aquatic ecosystems were observed. Two peaks were detected; the highest peak occurred in April in all four components and the second, smaller peak, occurred in August in plants and phytoplankton and in September in water and sediment (Figure 1). A marked decline in isolation rate occurred in components other than water, in the month of July.
Table 1. Abundance of V. cholerae non-01 in different components of the ponds. Pond no.
Sample Plant
Water
Phyloplankton
Soil sediment
Total
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
1 2 3 4 5
0/24 7/24 7/24 4/24 16/24
0 29 29 17 67
0/24 21/24 18/24 13/24 21/24
0 88 75 54 88
0/24 17/24 12/24 8/24 19/24
0 71 50 33 79
0/24 4/24 5/24 3/24 6/24
0 17 21 13 25
0/96 49/96 42/96 28/96 62/96
0 51 44 29 65
Total
34/120
28
73/120
61
56/120
47
18/120
15
181/480
38
NP--Number of samples positive for V. cholerae non-01. NT--Number of sample tested.
WorldJournalof Microbiologyand Bio~echnology,Vol 8, 1992
161
Seasonality and toxigenicity of V. cholerae Table 2. Enterotoxigenlclty tests with culture filtrates of V. cholerae non-01. Source of isolates
Y1 adrenal cell assay No. of filtrates cytotoxic/ No. tested
Positive (%)
No. positive/ No. tested
Positive (%)
2/12 2/12 2/11 2/8 8/43
17 17 18 25 19
0/12 0/12 0/11 0/8 0/43
0 0 0 0 0
Plants Water Phytoplankton Soil Total
Discussion
The present investigation shows the seasonality of V. cholerae non-0I in plants, water, phytoplankton and soil sediment in four of five pond ecosystems in and around Dhaka city. The highest peak in isolation rates in all four components was during the summer. Our results agree with other studies conducted in England and U.S.A. (Blake et al. 1980; Lee et aL 1982). The presence of the V. cholerae non-01 in various components of pond ecosystems indicates that freshwater ponds may act as a reservoir for V. cholerae non-01 in the aquatic environment. The role of plants and phytoplankton in the survival and transmission of V. cholerae has been studied previously (Islam & Aziz 1981; Islam et al. 1984, 1989, 1990a,b). The presence of the bacteria in the ponds throughout most of the year may contribute to the endemicity of V. cholerae non-01 in Bangladesh. Khan e~ al. (1984) noted a correlation between the rate of isolation of V. cholerae non-01 from the aquatic environment in Dhaka and the incidence of V. cholerae non-01 diarrhoea treated in the local Clinical Research Centre. In contrast to ponds 2 to 5, V. cholerae non-01 was not isolated from pond No. 1 during the study period, which may be due to its acidic pH and low salinity. It is unclear if all V. cholerae non-01 strains are enterotoxigenic (Huq et al. 1980; Madden et al. 1981). Other virulence factors such as cytotoxicity and presence of permeability factors and haemolysins can also occur in these 90-
~" 7 0 Z
o 6o!
so 40 ,'/
~
--
,c--
-t
, ..
'
.,:/~
," /
#
" \
",,.
",
\
'L
RIL assay & GM1 ELISA
"
;:' ",, . , .
I/
bacteria. Only a proportion of V. cholerae non-01 produce cholera-like toxin (Kodama et al. 1984); according to the World Health Organization (1984), this toxin is produced by less than 10% of V. cholerae non-01 isolated from clinical sources and less than 1% of isolates from the environment. None of the 43 strains selected in the present study for testing demonstrated cholera toxin-like activity, which is in agreement with other studies (Madden et al. 1981). Kaper e~ aL (1979) demonstrated that 87% of the V. cholerae non-01 strains isolated from the Chesapeake Bay exhibited cytotoxic activity in YI adrenal cells, compared with 18.6% of strains in our study. The presence of V. cholerae non-01 in all components of pond ecosystems most of the year demonstrated that untreated water from these sources was unfit for human consumption. Yet these water sources are routinely used for cooking, bathing and washing by local people. Studies in Bangladesh have shown that the use of safe drinking water from tube-wells did not reduce the incidence of cholera infection and this was attributed to the use of contaminated surface water (Sommer & Woodward 1972). The persistence of V. cholerae non-01 in ponds which are extensively used indicates a possible source of infection. The increased incidence of diarrhoea in the summer may be related to the observed increase in vibrio populations in the ponds at the time. The persistence of vibrios in the environment and the yearly recurrence of outbreaks of disease have never been adequately explained. Our study, by defining some of the ecological niches exploited by V. cholerae non-01, may begin to identify important links in the pathways of transmission of these organisms. This study gives some insight into the risk of contracting infections from aquatic environments and has relevance to the epidemiology of V. cholerae non-01 diarrhoea in Bangladesh.
~,/'X \
Acknowledgements JAN
FEE] M A R
A P R MAY
JUN
JUL
AUG
SEP
OCT
NOv
DEC
Figure 1. Seasonal changes in isolation rate (%) of V. cholerae non-01 from water ( 1 ) , phytoplankton (C)), soil sediment ( A ) and plant (D) samples.
162
World Journal af Microbiology and Biotechnology, Vol 8, I992
This research was supported by the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B). ICDDR, B is supported by countries and agencies which
M.S. b/am, M,]. A/am and P.K.B. Neogi share its concern about the impact of diarrheal diseases in the developing countries. Current donors giving assistance to the ICDDR, B are: Australia, Bangladesh, Belgium, France, Japan, The Netherlands, UK. The Canadian International Development Agency (CIDA), The Canadian International Development Research Centre (IDRC), The Danish International Development Agency (DANIDA), The Ford Foundation, The Norwegian Agency for International Development (NOR&D), The Swedish Agency for Research Cooperation with Developing Countries (SAREC), The Swiss Development Cooperation (SDC), United Nations Development Programme (UNDP), UNICEF, United Nations Capital Development Fund (UNCDF), US Agency for International Development (USAID), W H O and The World University Service of Canada (WUSC). The authors are grateful to Drs S. Tzipori and Chris Wankie for reviewing the manuscript. Many thanks to Mr Manzurul Haque for typing the manuscript.
References Aldova, E., Laznickova, K., Stepankova, E. & Lietava, J. 1968 Isolation of nonagglutinable vibrios from an enteritis outbreak in Czechoslovakia. Journal of Infectious Diseases 118, 25-31. Blake, P.A., Weaver, R.E. & Hollis, D.G. 1980 Diseases of humans (other than cholera) caused by Vibrios. Annual Review of Microbiology 34, 341-367. ColwelL R.R., Kaper, J. & Joseph, S.W. 1977 Vibrio cholerae, Vibrio parahaemolyticus, and other vibrios: occurrence and distribution in Chesapeake Bay. Science 198, 394-396. De, S.N. & Chatterjee, D.N. 1953 An experimental study of the mechanism of action of Vibrio cholerae on the intestinal mucus membrane. Journal of Pathology and Bacteriology 66, 559-562. Dutt, A.K., Alwi, S. & Velanthan, T. 1971 A shellfish-borne cholera outbreak in Malaysia. Transactions of the Royal Society of Tropical Medicine and Hygiene 65, 815-818. Hughes, J.M., Hollis, D.G., Gangarosa, E.J. & Weaver, R.E. 1978 Non-cholera vibrio infections in the United States, clinical, epidemiologic and laboratory features. Annals of Internal Medicine 88, 602-606. Huq, M.I., Alam, A.K.M.J., Brenner, D.J. & Morris, G.K. 1980 Isolation of vibrio-like group, EF-6, from patients with diarrhoea. Journal of Clinical Microbiology 11, 621-624. Islam, M.S. & Aziz, K.M.S. 1981 Association of vibrios with some hydrophytic plants. Bangladesh Journal of Microbiology 1, 70-72. Islam, M.S., Drasar, B.S. & Bradley, D.J. 1984 Survival of Vibrio cholerae 01 in artificial aquatic ecosystems. Journal of Medical Microbiology 18, 8. Islam, M.S., Drasar, B.S. & Bradley, D.J. 1989 Attachment of toxigenic Vibrio cholerae 01 to various freshwater plants and survival with a filamentous green alga, Rhizoclonium fontanum. Journal of Tropical Medicine and Hygiene 92, 396-401. Islam, M.S., Drasar, B.S. & Bradley, D.J. 1990a Long term persistence of toxigenic Vibrio cholerae 01 in the mucilaginous sheath of a blue green alga, Anabaena variabilis. Journal of Tropical Medicine and Hygiene 93, 133-139. Islam, M.S., Drasar, B.S. & Bradley, D.J. 1990b Survival of toxigenic Vibrio cholerae 01 with a common duckweed, Lemna minor, in artificial aquatic ecosystems. Transactions of the Royal Society of Tropical Medicine and Hygiene 84, 422-424.
Kaper, J., Lockman, H., ColwelL R.R. & Joseph, S.W. 1979 Ecology, serology and enterotoxin production of Vibrio cholerae in Chesapeake Bay. Applied and Environmental Microbiology 37, 91-I03. Kenyon, J.E., Piexoto, D.R., Austin, B. & Gillies, D.C. 1984 Seasonal variation in numbers of Vibrio cholerae (non-01) isolated from California coastal waters. Applied and Environmental Microbiology 47, 1243-1245. Khan, M.U., Shahidullah, M., Haque, M.S. & Ahmed, W.U. 1984 Presence of vibrios in surface water and their relation with cholera in a community. Tropical and Geographical Medicine 36, 335-340. Kodama, H., Gyobu, Y., Tokuman N., Okada, 1., Uetake, H., Shimada, T. & Sanazaki, R. 1984 Ecology of non-01 Vibrio cholerae in Toyama prefecture. Microbiology and Immunology 28, 311-325. Lee, J.V. 1985 Vibrio, Aeromonas and Plesiomonas. In Detection and Isolation of Microbes of Medical and Veterinary Importance, eds Skinner, F.S. & Collins, C.H. pp. 13-33. London: Academic Press. Lee, J.V., Bashford, D.J., Donovan, T.J., Fumiss, A.L. & West, P.A. 1982 The incidence of Vibrio cholerae in water, animals and birds in Kent, England. Journal of Applied Bacteriology 52, 281-291. Madden, J.M., Nematollahi, S.P., Hill, W.E., McCardell, B.A. & Twedt, R.M. 1981 Virulence of three clinical isolates of Vibrio cholerae non-01 serogroup in experimental enteric infections in rabbits. Infection and Immunity 33, 616--619. Mclntyre, O.R., Feeley, J.E., Greenough, III, W.B., Bnenenson, A.S., Hasan, S.I. & Saad, A. I965 Diarrhoea caused by non-cholera vibrios. American Journal of Tropical Medicine 14, 412-418. Monsur, K.A. 1961 A highly selective gelatin-taurocholate-tellurite medium for the isolation of Vibrio cholerae. Transactions of the Royal Society of Tropical Medicine and Hygiene 55, 440-445. Prats, G., Mirelis, B., Pericas, R. & Verger, G. 1975 Non-cholera vibrio septicaemia and meningoencephalitis. Annals of Internal Medicine 82, 448-449. Richardson, S.H. 1969 Factors influencing in vitro skin permeability factor produced by Vibrio cholerae. Journal of Bacteriology 100, 27-34. Sack, D.A. & Sack, R.B. 1975 Test for enterotoxigenic Escherichia coli using Y1 adrenal cells in miniculture. Infection and Immunity 11, 334-336. Sack, D., Huda, S., Neogi, P.K.B., Daniel, R.R. & Spira, W.M. 1980 Microtiter ganglioside enzyme linked immunosorbent assay for Vibrio and Escherichia colt heat-labile enterotoxins and antitoxin. Journal of Clinical Microbiology 11, 35-40. Sommer, A. & Woodward, W.E. 1972 The influence of protected water supplies on the spread of Classical/Inaba and El Tor/Ogawa cholera in rural East Bengal. Lancet 2, 985-987. West, P.A. & Colwell, R.R. I984 Identification and classification of Vibrionaceae--an overview. In Vibrios in the Environment, ed Colwell, R.R., pp. 285-363, New York: John Wiley & Sons. World Health Organization. 1984 Report of the Third Meeting of
Scientific Working Group on Bacterial Enteric Infections: Microbiology, Epidemiology, Immunology and Vaccine Development. pp. 1-17. Geneva: World Health Organization. Zafari, Y., Zarifi, A.Z., Rahmanzadeh, S. & Fakhar, N. I973 Diarrhoea caused by non-agglutinable Vibrio cholerae (noncholera vibrio). Lancet 2, 429-430. Zinnaka, Y. & Carpenter, Jr, C.C.J. I972 An enterotoxin produced by non-cholera vibrios. Johns Hopkins Medical Journal 81, 403-411.
(Received in revised form 2 August 199I; accepted 24 August 199I)
World Journal of Microbiology and Biotechnology, Vol 8, I992
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Seasonality and toxigenicity of Vibrio cholerae non-01 isolated from different components of pond ecosystems of Dhaka City, Bangladesh M.S. Islam,* M.J. Alam and P.K.B. Neogi Diarrhoea due to Vibrio cholerae non-01 is common in Bangladesh. Four hundred and eighty samples, including plants, water, phytoplankton and sediment, were collected from five ponds in Dhaka every 15 days for one year. V. cholerae non-01 was isolated from 181 (38%) of the samples. Two peaks were evident: one in April and the other in August/September. Forty-three (23%) of the 181 isolates were examined for toxigenicity and 19% were cytotoxic to Y1 adrenal cells. This study provides evidence of the likely infectious nature of some ponds and may have relevance to the epidemiology of diarrhoea caused by V. cholerae non-01 in Bangladesh. Key words: Diarrhoea, seasonality, toxigenicity, Vibrio.
Vibrio cholerae non-01 is a causative agent of moderate-tosevere, cholera-like diarrhoea in Bangladesh and other parts of the world (Mclntyre el al. 1965; Zafari el al. 1973; Hughes et al. 1978). Strains of V. cholerae non-01 are morphologically and biochemically similar to those of V. cholerae 01 but are distinguished by lack of agglutination with group 01 antiserum (ColweU et al. 1977). Food-borne and water-borne outbreaks due to V. cholerae non-01 have been reported from various countries, including Czechoslovakia, Sudan, Saudi Arabia and India (Aldova et al. 1968; Zafari et al. 1973). Epidemics due to V. cholerae non-01 have also been reported during cholera outbreaks (Mclntyre et al. I965; Dutt et al. 1971). These organisms have been isolated from septicaemic and meningoencephalitis patients (Prats el al. 1975). The enterotoxigenicity of V. cholerae non-01 demonstrated in the rabbit ileal loop (RIL) assay and by other methods indicates that these strains are potential pathogens (Zinnaka & Carpenter 1972). The enterotoxin produced by V. cholerae non-01 is closely related to cholera toxin produced by classical V. cholerae 01 (Kaper et al. 1979). The ecology of V. cholerae non-01 has been studied in
M. S. Islam and P. K. B. Neogi are with the international Center for Diarrboeal Diseases Research, Bangladesh, GPO Box 128, Dhaka 1000, Bangladesh. M. J. Alam is with the Department of Microbiology, University of Dhaka, Bangladesh. *Corresponding author.
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World ]ournaI of Microbiology and Biotechnology, Vol 8, 1992
the Chesapeake Bay and California coastal waters (Colwell el al. 1977; Kenyon el al. 1984). These studies demonstrated a link between the number of organisms and water temperature. In Bangladesh, Khan et a]. (1984), in investigating the role of surface water as a possible reservoir of V. cholerae non-01 in the environment, found the bacteria in approximately 30% of samples tested. However, other components such as plants, plankton and sediment were not evaluated as possible reservoirs nor was the seasonality of the organisms documented. Moreover the organisms recovered were not examined for virulence factors. Therefore, in the present study we examined the seasonality of V. cholerae non-01 in the various components of the aquatic environment in addition to surface water and evaluated the toxigenicity of the isolated strains.
Materials and Methods Description of Ponds The surface area and depth of all ponds ranged from 1900 to 6000 m2 and 1.5 to 5.2 m, respectively. The water temperatures varied from 18 to 34~ and the salinities from O to 0.18~oo. In all except pond No. 1, the waters were alkaline and used by large numbers of people every day for bathing and washing. All ponds were over-flooded during the 1988 flood.
M.S. Islam, M.]. Alam and P.K.B. Neogi inoculation, animals were sacrificed and the results were expressed as the accumulated fluid volume in ml per cm of loop.
Collection of Samples Samples of water, plants, phytoplankton and sediments from five ponds in and around Dhaka city, Bangladesh, were collected every 15 days, between May 1988 and April 1989. Plants (Eichhornia crassipes, Nympkoides sp. and Telanthera philoxeroides) were collected and kept in polyethylene bags. Samples of water, each of 500 ml, were collected in pre-sterilized 500 ml narrow-mouth, plastic bottles. Phytoplankton was collected using plankton nets and kept in 120 rnl glass bottles. All field samples were transported to the laboratory inside an insulated ice-box with cool packs and processed within 6 h of collection. Sediment was collected with a core sampler and kept in 120 ml glass bottles.
GM1 ELISA. The presence of cholera toxin was assayed using the
GMIganglioside ELISAaccording to the method described by Sack et al. (1980). YI Adrenal Cell Assay. The filtrates were added to Y1 adrenal cells plated in 96-well plates 24 h previously and incubated at 37~ in 7% CO 2, as described by Sack & Sack (1975). After 24 h, cells were examined for cytotoxic and cytotonic effects.
Processing of Samples Plant material (10 g) was homogenized in 100 ml of sterile 0.9% saline in a Waring blender. Phytoplankton samples (I0 ml) were homogenized in a Teflon-tipped tissue grinder (Wheaton Scientific, Millville, NJ) using a Sted Fast stirrer (Model 300, Fisher Scientific, USA). One ml of the plant homogenate, 10 ml of phytoplankton homogenate, 50 ml of each water sample and 1.0 g of sediment were enriched separately in bile salts peptone broth and incubated overnight at 37~ All samples were then plated onto thiosulphate citrate bile salts sucrose (TCBS) agar and taurocholate tellurite gelatin agar and incubated at 37~ for 18 to 24 h (Monsur 1961). Suspected vibrio colonies were further characterized using standard procedures (West & Colwell 1984; Lee 1985). Enterotoxin Assays Bacterial Isolates. Forty-three isolates of 17. cholerae non-01 were selected randomly and tested for toxigenicity using three assays. The strains were isolated from plants, water, phytoplankton and sediment samples. Preparation of Culture Filtrates. The test strains were each grown in 10 ml of Richardson's medium in 50 ml conical flasks (Richardson 1969). The flasks were incubated in a shaking water bath with 100 rev/min for 16 h at 37~ The cultures were centrifuged at 10,000 x g for 30 min. The supematants were filtered through 0.22 pm pore membrane filters and stored at -20~ for use in the following assays. Rabbit ileal Loop (RIL) Assay. One ml of culture filtrate from each of the test strains was inoculated into a 4 to 6 cm length of ileal loop from 1.5 to 2.0kg New Zealand white rabbits (De & Chatterjee 1953). Each strain was tested in duplicate. Vibrio cholerae 01 strain 569B was used as a positive control. Eighteen hours after
Results Vibrio choIerae non-01 was isolated from 18I (38%) of the 480 environmental samples collected (Table I), of which pond No. 5 had the highest isolation rate of 62 from 96 samples collected (65%). In contrast, no organisms were recovered from any of the 96 samples collected from pond No. i. Pond No. 5 also yielded most organisms in each of the four sample types: 87% of water samples, 80% of phytoplankton, 67% of the plants and 25% of the soil sediment samples were positive (Table 1). The toxigenicities of 43 strains randomly selected for testing are shown in Table 2. Twelve strains isolated from plants, 12 from water, 11 from phytoplankton and eight from soil were tested. Overall, eight strains (19%) were cytotoxic for Y1 adrenal cells. No cytotonic activity was detected in the Y1 adrenal cell assay. All strains were also negative in the GM~ ELISA and RIL assays. Distinct seasonal patterns of isolation of V. cholerae non-01 in the four components of the aquatic ecosystems were observed. Two peaks were detected; the highest peak occurred in April in all four components and the second, smaller peak, occurred in August in plants and phytoplankton and in September in water and sediment (Figure 1). A marked decline in isolation rate occurred in components other than water, in the month of July.
Table 1. Abundance of V. cholerae non-01 in different components of the ponds. Pond no.
Sample Plant
Water
Phyloplankton
Soil sediment
Total
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
NP/NT
(%)
1 2 3 4 5
0/24 7/24 7/24 4/24 16/24
0 29 29 17 67
0/24 21/24 18/24 13/24 21/24
0 88 75 54 88
0/24 17/24 12/24 8/24 19/24
0 71 50 33 79
0/24 4/24 5/24 3/24 6/24
0 17 21 13 25
0/96 49/96 42/96 28/96 62/96
0 51 44 29 65
Total
34/120
28
73/120
61
56/120
47
18/120
15
181/480
38
NP--Number of samples positive for V. cholerae non-01. NT--Number of sample tested.
WorldJournalof Microbiologyand Bio~echnology,Vol 8, 1992
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Seasonality and toxigenicity of V. cholerae Table 2. Enterotoxigenlclty tests with culture filtrates of V. cholerae non-01. Source of isolates
Y1 adrenal cell assay No. of filtrates cytotoxic/ No. tested
Positive (%)
No. positive/ No. tested
Positive (%)
2/12 2/12 2/11 2/8 8/43
17 17 18 25 19
0/12 0/12 0/11 0/8 0/43
0 0 0 0 0
Plants Water Phytoplankton Soil Total
Discussion
The present investigation shows the seasonality of V. cholerae non-0I in plants, water, phytoplankton and soil sediment in four of five pond ecosystems in and around Dhaka city. The highest peak in isolation rates in all four components was during the summer. Our results agree with other studies conducted in England and U.S.A. (Blake et al. 1980; Lee et aL 1982). The presence of the V. cholerae non-01 in various components of pond ecosystems indicates that freshwater ponds may act as a reservoir for V. cholerae non-01 in the aquatic environment. The role of plants and phytoplankton in the survival and transmission of V. cholerae has been studied previously (Islam & Aziz 1981; Islam et al. 1984, 1989, 1990a,b). The presence of the bacteria in the ponds throughout most of the year may contribute to the endemicity of V. cholerae non-01 in Bangladesh. Khan e~ al. (1984) noted a correlation between the rate of isolation of V. cholerae non-01 from the aquatic environment in Dhaka and the incidence of V. cholerae non-01 diarrhoea treated in the local Clinical Research Centre. In contrast to ponds 2 to 5, V. cholerae non-01 was not isolated from pond No. 1 during the study period, which may be due to its acidic pH and low salinity. It is unclear if all V. cholerae non-01 strains are enterotoxigenic (Huq et al. 1980; Madden et al. 1981). Other virulence factors such as cytotoxicity and presence of permeability factors and haemolysins can also occur in these 90-
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bacteria. Only a proportion of V. cholerae non-01 produce cholera-like toxin (Kodama et al. 1984); according to the World Health Organization (1984), this toxin is produced by less than 10% of V. cholerae non-01 isolated from clinical sources and less than 1% of isolates from the environment. None of the 43 strains selected in the present study for testing demonstrated cholera toxin-like activity, which is in agreement with other studies (Madden et al. 1981). Kaper e~ aL (1979) demonstrated that 87% of the V. cholerae non-01 strains isolated from the Chesapeake Bay exhibited cytotoxic activity in YI adrenal cells, compared with 18.6% of strains in our study. The presence of V. cholerae non-01 in all components of pond ecosystems most of the year demonstrated that untreated water from these sources was unfit for human consumption. Yet these water sources are routinely used for cooking, bathing and washing by local people. Studies in Bangladesh have shown that the use of safe drinking water from tube-wells did not reduce the incidence of cholera infection and this was attributed to the use of contaminated surface water (Sommer & Woodward 1972). The persistence of V. cholerae non-01 in ponds which are extensively used indicates a possible source of infection. The increased incidence of diarrhoea in the summer may be related to the observed increase in vibrio populations in the ponds at the time. The persistence of vibrios in the environment and the yearly recurrence of outbreaks of disease have never been adequately explained. Our study, by defining some of the ecological niches exploited by V. cholerae non-01, may begin to identify important links in the pathways of transmission of these organisms. This study gives some insight into the risk of contracting infections from aquatic environments and has relevance to the epidemiology of V. cholerae non-01 diarrhoea in Bangladesh.
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Acknowledgements JAN
FEE] M A R
A P R MAY
JUN
JUL
AUG
SEP
OCT
NOv
DEC
Figure 1. Seasonal changes in isolation rate (%) of V. cholerae non-01 from water ( 1 ) , phytoplankton (C)), soil sediment ( A ) and plant (D) samples.
162
World Journal af Microbiology and Biotechnology, Vol 8, I992
This research was supported by the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B). ICDDR, B is supported by countries and agencies which
M.S. b/am, M,]. A/am and P.K.B. Neogi share its concern about the impact of diarrheal diseases in the developing countries. Current donors giving assistance to the ICDDR, B are: Australia, Bangladesh, Belgium, France, Japan, The Netherlands, UK. The Canadian International Development Agency (CIDA), The Canadian International Development Research Centre (IDRC), The Danish International Development Agency (DANIDA), The Ford Foundation, The Norwegian Agency for International Development (NOR&D), The Swedish Agency for Research Cooperation with Developing Countries (SAREC), The Swiss Development Cooperation (SDC), United Nations Development Programme (UNDP), UNICEF, United Nations Capital Development Fund (UNCDF), US Agency for International Development (USAID), W H O and The World University Service of Canada (WUSC). The authors are grateful to Drs S. Tzipori and Chris Wankie for reviewing the manuscript. Many thanks to Mr Manzurul Haque for typing the manuscript.
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Scientific Working Group on Bacterial Enteric Infections: Microbiology, Epidemiology, Immunology and Vaccine Development. pp. 1-17. Geneva: World Health Organization. Zafari, Y., Zarifi, A.Z., Rahmanzadeh, S. & Fakhar, N. I973 Diarrhoea caused by non-agglutinable Vibrio cholerae (noncholera vibrio). Lancet 2, 429-430. Zinnaka, Y. & Carpenter, Jr, C.C.J. I972 An enterotoxin produced by non-cholera vibrios. Johns Hopkins Medical Journal 81, 403-411.
(Received in revised form 2 August 199I; accepted 24 August 199I)
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